1. Field of the Invention
The present invention relates generally to multi-node sensor systems. More specifically, the present invention relates to a system, program product, and related methods to monitor the health of structural components.
2. Description of the Related Art
Various types of platforms such as, for example, aircraft structural components, aircraft skins, or other related components when in operation are subjected to various environmental conditions such as stress and strain, exposure to temperature extremes, and/or significant vibration energy. Due to the various environmental conditions such components can suffer material degradation over time. Structural health monitoring helps promote realization of the full potential of such components.
Traditionally, structural monitoring has relied upon using ultrasound techniques on the structure prior to installation (not in situ). More recently, remotely positioned sensors units or nodes have been installed adjacent to such structures/components to monitor various parameters such as, for example, strain levels, stress, temperature, pressure, or vibration level to help manage physical inspection schedules, maintenance schedules to help predict material failure and to generally monitor the “health” of such components.
Such nodes have been provided a dedicated power supply through conductors, e.g., wires, connected to the aircraft/vehicle electrical system or through chemical batteries. Similarly, the nodes have been provided communication through conductors, e.g., wires or optical fiber. Such wiring can undesirably result in increased weight and complexity of the component being monitored and/or of the associated structure or component and are subject to damage or breakage requiring extensive repair costs and down time.
Other structural health monitoring systems include self-powered sensors/nodes attached to or embedded within the components to be monitored that can reduce dependence on batteries or any other external power source and can negate the need for a “wired” communication pathways. Such sensors can be relatively small in size and can utilize energy obtained or otherwise transmitted through the component or structure being monitored as both a power and data source.
Data capturing systems, such as that employing radiofrequency identification, can also be used in health monitoring. Such systems can include both active and passive wireless communication schemes. The active wireless sensors/nodes can provide a continuous or intermittent stream of sampled raw data indicating parameters of the component or structure being monitored. The data is typically collected by a central collector or by a series of intermediate collectors which provide such data to a central collector. The passive wireless sensors can also collect a continuous or intermittent stream of sampled raw data indicating parameters of the component or structure being monitored. The passive sensors, however, do not actively transmit such data, but instead receive energy from an interrogation unit, which provides power to extract the sensor data. The passive wireless sensors are most often utilized in applications where ultra low power communication is desired. In such passive systems, an interrogator can transmit a signal to each passive wireless sensor to power the sensor and to transmit a request for data.
Conventional systems do not have provisions for correlating the outputs of a multiplicity of health monitoring sensor nodes in both space and time to infer a state of health of a structure that cannot be otherwise obtained using the non-correlated output of the sensor nodes. For example, there exists systems having sensors that can determine the existence and possibly the location of a bird strike, for example, due to an associated acoustic emission, but cannot correlate sensor data to determine or infer the damage caused by the bird strike or other damage such as delamination or material fatigue. Further, even detection of the location of damage using acoustic emissions can be difficult if not impossible where the damage is equally spaced from any surrounding sensors. There also exists systems which can detect acceleration, stress, strain, or pressure and therefore can determine if a corresponding acceleration, stress, strain, or pressure limit has been exceeded. Such systems, however, primarily derive their data from a single sensor, and thus, cannot correlate such data to infer damage that will eventually result in exceeding such a limit prior to actually exceeding such limits.
In a multi-sensor node wireless monitoring application, it is often necessary to relate events seen by one sensor node to events seen by another. This requires complicated and power hungry clock distribution or synchronization techniques for timing and complicated algorithms for relating the data to the structure. Moreover time synchronization typically can require an explicit clock distribution, e.g., real-time clock, or direct wiring. To alleviate such problems, some systems have eliminated any data correlation, resulting in the data from all the different nodes being processed independently without any knowledge of what the rest of the system is experiencing. In such implementation, typically the system uses point-to-point communication with no data correlation between the nodes. The Applicants have recognized that reduction of system functionality and flexibility generally results from such techniques.
Recognized by the Applicants, therefore, is the need to provide a wireless multi-sensor node structural health monitoring system that can correlate structural health data from multiple sensor nodes both in time and in space, allowing a more complete view of the health of the structure. Also recognized is the need to provide multi-sensor node health monitoring system that provides an ability to detect damage and identify a failure location without the need to remove external structural components, without the need for a real-time clock, and without the need for complicated data synchronization algorithms.